Arris S33 modem w/ Xfinity 1.2Gbps service

Just started using an Arris S33 modem for my Xfinity 1.2Gbps link.  After reboot I get ~900Mbps downstream and ~6Mbps upstream.  Hours later I am getting ~25Mbps downstream ~4Mbps upstream.  I have checked the S33 cable signal levels and they look to be within expectations.  Is there anything else I need to check before heading deeper into the Xfinity support forest?